Lamp assemblies incorporating reflectors are well known. Examples include spotlights and floodlights for indoor and outdoor use. Typically, a lamp is mounted in a sealed outer envelope. The outer envelope includes a reflecting interior surface, typically parabolic, for directing light in a preferred direction. The reflector is covered with a lens, and a base is provided for mounting the lamp assembly and for interconnection of the lamp to a source of electrical energy. Incandescent lamps, high pressure sodium lamps and mercury lamps have been utilized in such lamps assemblies.
Recently, it has been proposed to utilize metal halide arc discharge lamps in reflector-type lamp assemblies. Metal halide lamps provide excellent color, long life and high efficiency. Low wattage metal halide arc lamps include a generally cylindrical arc tube enclosing a suitable fill material such as sodium, scandium and mercury iodides. Electrodes are sealed in opposite ends of the arc tube, and electrode leads extend through press seals for connection to an electrical source.
In a lamp wherein a metal halide lamp is mounted in a reflector, several requirements must be met. It is preferred, in order to maximize light output, that the axis of the arc tube be aligned with the optical axis of the reflector and that the center of light output from the arc tube coincide with the focal point of the reflector. In mounting the metal halide lamp in the reflector, it is not feasible to attach a lamp support to the lens. Therefore, the arc lamp must be supported entirely from the base end.
It is well known that conductors located in proximity to an arc discharge tube containing sodium cause sodium migration or sodium electrolysis. Sodium ions migrate through the wall of the arc discharge tube and thereby reduce the life of the lamp. It is therefore desirable to keep conducting frame members and power leads away from the arc tube to the extent possible. In prior lamp assemblies, a "frameless" construction has been utilized in which a fine wire connects the electrode at the dome end of the arc tube to the electrical feedthrough at the base end of the lamp. The arc tube is supported by bulb spacers positioned at the base and dome ends of the bulb. The electrically isolated floating frame develops a positive charge which opposes the migration of sodium ions through the arc tube. As noted above, the double-ended mechanical mount is not feasible in a reflector-type assembly.
It has been found desirable to operate metal halide arc discharge lamps in a light transmissive quartz shroud or shield. The shroud substantially surrounds the arc tube and produces a higher and more uniform arc tube temperature than would otherwise occur. The shroud is in part responsible for the excellent color temperature and long operating life of the metal halide arc lamp. In addition, it is known that metal halide arc tubes are subject to burst on rare occasions. The shroud functions to contain shards of the arc tube when a burst occurs. The mounting arrangement for the arc tube must provide means for mounting both the shroud and the arc tube.
It is a general object of the present invention to provide improved reflector lamp assemblies.
It is another object of the present invention to provide reflector lamp assemblies which utilize metal halide arc discharge lamps.
It is a further object of the present invention to provide a metal halide reflector lamp assembly having long operating life.
It is a further object of the present invention to provide a lamp assembly, including a metal halide lamp surrounded by a light-transmissive shroud, suitable for mounting in a reflector.
It is yet another object of the present invention to provide a metal halide lamp assembly wherein all conductive parts except the electrical inleads are electrically isolated.
It is a further object of the present invention to provide a lamp assembly including a metal halide arc lamp mounted in a reflector, that is easily manufactured and low in cost.